Differential kinematics and singularities of a quadruple-end-effector 9-DOF 3-5R planar parallel robot for multi-tasking operations

Multi-tasking is crucial to enhance the productivity of robotic systems. Moreover, it is compulsory in many applications. Motivated by these facts, this paper studies a parallel robot with four end-effectors. It is a 9-DOF planar parallel manipulator (PPM) whose moving platform is connected to the base by three serial 5R legs. The moving platform, which is one of the end-effectors, is a triangular plate having two translational and one rotational DOFs. Each of the other three end-effectors is fixed to one different leg and has two translational DOFs. In comparison to its two possible alternatives, namely, a 9-RRR PPM with configurable platform, or a cooperative multi-robot system composed of three 5R and one 3-RRR PPMs, the quadruple-end-effector 3-5R PPM is optimal in terms of the number of links, the number of joints and the number of independent loops. The differential kinematics and singularities of this 9-DOF tripod are analyzed. Moreover, one of its potential applications is demonstrated through numerical simulation. Thanks to its ability of simultaneous execution of four tasks, the studied robot is promising for use in numerous industrial and medical operations.